Soil/Landform Unit 119

Aerial view of the gently undulating basalt plains near Bannockburn

Area:

32 119 ha

2.40% of CMA region

This large unit has a few major occurrences in the Lethbridge, Bannockburn and Mount Pollock areas. As part of the volcanic Western Plains, this unit comprises landform components including stony undulating rises, and depressions and flats. The soils of this unit include neutral and alkaline shallow self-mulching clays (

Vertosols

often strongly

sodic

) and minor (strongly sodic)

mottled

black texture contrast soils (

Sodosols

) intermingled on the flats. Rainfall decreases to the north-east. Land use is grazing (sheep) and cropping including horticulture (dominant in some areas). This unit is susceptible to waterlogging and

compaction

where a lighter upper soil occurs. The expansive clays may stress root systems and limit workability timing, but black surface soils provide a

friable

seedbed. Some areas are also susceptible to sheet and rill erosion (dissected unit edges) and structure decline with the strongly sodic subsoils and surface soils.

Gently undulating basalt plain
	Grazing is a common land use of this soil-landform unit

Component	1	2
Proportion of soil-landform unit	70%	30%
CLIMATE Rainfall (mm)	Annual: 590
Temperature (^oC)	Minimum 9, Maximum 19
Precipitation less than potential evapotranspiration	October-April
GEOLOGY Age and lithology	Quaternary basalt and alluvium
Geomorphology	6.1.3 Volcanic Western Plains with poorly developed drainage
LANDUSE	Uncleared areas: Nature conservation Cleared areas: Sheep and beef cattle grazing; cropping (cereal); softwood plantations
TOPOGRAPHY Landscape	Undulating basalt rises
Elevation range (m)	19-273
Local relief (m)	10
Drainage pattern	Dendritic
Drainage density (km/km²)	0.8
Landform	Rises	Plain
Landform element	Undulating stony rises	Flats/depressions
Slope and range (%)	3 (1-5)	1 (0-3)
Slope shape	Convex	Straight
NATIVE VEGETATION Ecological Vegetation Class	Plains Grassland (0.3%)
SOIL Parent material	Basalt	Basaltic colluvium and alluvium
Description (Corangamite Soil Group)	Neutral and alkaline shallow self-mulching clays (39)	Alkaline deep or shallow grey cracking clays (39)
Soil type sites	SFS2, SW89, SFS1	SFS2, MM5154, SW89
Surface texture	Light clay	Light clay
Permeability	Low	Very low
Depth (m)	>2	>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Uniform expansive clay soil, high water holding capacity and nutrient holding capacity. Shallow soil, stones common. Cracking soil, black soil may have self-mulching surfaces. Low to moderate permeability once moist, sodic (often strongly) subsoil. Slow site drainage.	Uniform expansive clay soil, high to very high water holding capcity and nutrient holding capacity. Deep, few stones. Cracking soil, black soil may have self-mulching surfaces where it occurs. Low permeability once moist, sodic (often strongly) subsoi. Very slow site drainage.

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